Antifogging Coatings Research Articles

Preparation of Water-Resistant Antifog Hard Coatings on Plastic Substrate

A novel water resistant antifog (AF) coating for plastic substrates was developed, which has a special hydrophilic/hydrophobic bilayer structure. The bottom layer, acting both as a mechanical support and a hydrophobic barrier against water penetration, is an organic-inorganic composite comprising colloidal silica embedded in a cross-linked network of dipentaethritol hexaacrylate (DPHA). Atop this layer, an AF coating is applied, which incorporates a superhydrophilic species synthesized from Tween-20 (surfactant), isophorone diisocyanate (coupling agent), and 2-hydroxyethyl methacrylate (monomer). Various methods, e.g., FTIR, SEM, AFM, contact angle, and steam test, were employed to characterize the prepared AF coatings. The results indicated that the size and the continuity of the hydrophilic domains on the top surface increased with increasing added amount of T20, however, at the expense of hardness, adhesiveness, and water resistivity. The optimal T20 content was found to be 10 wt %, at which capacity the resultant AF coating was transparent and wearable (5H, hardness) and could be soaked in water for 7 days at 25 °C without downgrading of its AF capability.

In situ Assembly of Raspberry- and Mulberry-like Silica Nanospheres toward Antireflective and Antifogging Coatings

Raspberry- and mulberry-like hierarchically structured silica particulate coatings were fabricated via facile in situ layer-by-layer assembly with monodisperse silica nanoparticles (NPs) of two different sizes followed by calcination. Raspberry-like and mulberry-like silica particulate coatings were achieved when the size ratio of two silica particles was 20/200 and 20/70 nm, respectively. The latter coating exhibited good antireflective property. Its maximum transmittance reached as high as 97%, whereas that of the glass substrate is only 91%. The morphologies of the coatings were observed by scanning electron microscopy and atom force microscopy. The surface properties of these coatings were investigated by measuring their water contact angles and the spreading time of water droplet. The results showed that such hierarchically structured coatings had superhydrophilic and antifogging properties.

Characterization of Multilayer Anti-Fog Coatings

Fog formation on transparent substrates constitutes a major challenge in several optical applications requiring excellent light transmission characteristics. Anti-fog coatings are hydrophilic, enabling water to spread uniformly on the surface rather than form dispersed droplets. Despite the development of several anti-fog coating strategies, the long-term stability, adherence to the underlying substrate, and resistance to cleaning procedures are not yet optimal. We report on a polymer-based anti-fog coating covalently grafted onto glass surfaces by means of a multistep process. Glass substrates were first activated by plasma functionalization to provide amino groups on the surface, resulting in the subsequent covalent bonding of the polymeric layers. The anti-fog coating was then created by the successive spin coating of (poly(ethylene-maleic anhydride) (PEMA) and poly(vinyl alcohol) (PVA) layers. PEMA acted as an interface by covalently reacting with both the glass surface amino functionalities and the PVA hydroxyl groups, while PVA added the necessary surface hydrophilicity to provide anti-fog properties. Each step of the procedure was monitored by XPS, which confirmed the successful grafting of the coating. Coating thickness was evaluated by profilometry, nanoindentation, and UV visible light transmission. The hydrophilic nature of the anti-fog coating was assessed by water contact angle (CA), and its anti-fog efficiency was determined visually and tested quantitatively for the first time using an ASTM standard protocol. Results show that the PEMA/PVA coating not only delayed the initial period required for fog formation but also decreased the rate of light transmission decay. Finally, following a 24 hour immersion in water, these PEMA/PVA coatings remained stable and preserved their anti-fog properties.

Durable Antifog Films from Layer-by-Layer Molecularly Blended Hydrophilic Polysaccharides

Mechanically durable, long-lasting antifog coatings based on polysaccharides were developed using a layer-by-layer (LBL) assembly process. The unique properties of these coatings are a result of a molecular-level blending of the polysaccharides, with multilayers containing chitosan and carboxymethyl cellulose providing the best overall properties. The antifog properties resulted from a strong interaction between the polar and H-bonding elements of the assembled polymers and water molecules and the concomitant formation of thin films of water. Environmental scanning electron microscopy (ESEM) studies confirmed that fogging coatings are decorated with light scattering, micrometer-sized droplets of water whereas antifogging coatings remain droplet free. To improve the mechanical durability of the multilayer films on substrates, the surface was modified via self-assembly of epoxy-functionalized silane molecules. Cross-linking chemistry was then applied to improve the mechanical robustness of the LBL films on various surfaces. These films were characterized using several techniques: optical profilometery (PL), spectroscopic ellipsometry (EL), contact angle goniometry (CA), and atomic force microscopy (AFM). The antifog properties of the films were evaluated by several tests under different environmental conditions. This work demonstrates that the unique water-adsorbing properties of polysaccharides can be exploited to create permanent antifog properties, which may be useful for various applications.

Unusual Antibacterial Property of Mesoporous Titania Films: Drastic Improvement by Controlling Surface Area and Crystallinity

One of the most urgent requirements of human life in the 21 century is development of new antibacterial materials and sterilization technologies that can improve human health. Until now, the most commonly used antibacterial agents are based on chlorine, chlorine dioxide, and organic biocide compounds. These agents are extremely toxic for humans and their residues are also not environmentally friendly. Therefore, it is very important to develop antibacterial biocompatible materials. Titanium dioxide (titania, TiO2) materials in the anatase form have attracted great interest as a new antibacterial material. Titania can work well under ultraviolet (UV) light owing to its photo-semiconductor properties. Currently, this property has been widely utilized for various applications such as water treatment, air and environmental purification, hazardous waste remediation, and deactivation of bacteria. Commercial products with titania (e.g., self-cleaning glasses and anti-fogging coatings) are well known all over the world. To date, various titania-based nanostructures including nanorods and nanoparticles have been reported. To further enhance the photocatalytic performance, many efforts have been made for doping various metal/semiconductor elements into titania materials. In this system, the electrons accumulated on the metal and holes remained on the photocatalyst surface. Therefore, a significant reduction in the recombination rate is realized owing to better charge separation between the electrons and holes. Therefore, the titania-based composites with metal/semiconductor elements can enhance the overall photocatalytic efficiency and the damage of microorganisms of the cell. In this Communication, we focused on a further simple and low-cost synthetic method and synthesized mesoporous titania films by utilizing bottom-up nanotechnology with surfactant assembly. Mesoporous materials with extremely high surface area should be good candidates for the next generation of antibacterial materials. Compared with the traditional titania materials mentioned above, the high surface area originated from mesoporous networks can provide a higher amount of hydroxyl radicals (·OH) which can increase the photoactivity. In the past few years, special attention has been paid to the synthesis of mesoporous titania powders as effective photocatalysts including an antibacterial application. However, the mesoporous titania in the powder form has some disadvantages. The powders which are not fixed on substrates are washed out easily by external treatments and then the released particles themselves may pollute the environment. Also, nanosized powders generally cause serious problems to human health. Therefore, the mesoporous titania films reported here are more applicable [a] H. Oveisi, X. Jiang, Dr. Y. Nemoto, Prof. Dr. Y. Yamauchi World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki, 305-0044 (Japan) Fax: (+81)29-860-4706 E-mail : Yamauchi.Yusuke@nims.go.jp [b] Dr. S. Rahighi, Prof. Dr. S. Wakatsuki Structural Biology Research Center High Energy Accelerator Research Organization (KEK) 1-1 Oho, Tsukuba, Ibaraki, 305-0801 (Japan) [c] H. Oveisi, Prof. Dr. A. Beitollahi Center of Excellence in Advanced Materials and Processing Department of Metallurgy and Materials Engineering Iran University of Science and Technology (IUST) Narmak, Tehran 16844 (Iran) [d] X. Jiang, Prof. Dr. Y. Yamauchi Faculty of Science and Engineering Waseda University 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan) [e] Prof. Dr. Y. Yamauchi Precursory Research for Embryonic Science and Technology (PRESTO) Japan Science and Technology Agency (JST) 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan). [] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000351.

Recent developments in bio-inspired special wettability

Nature is a school for scientists and engineers. After four and a half billion years of stringent evolution, some creatures in nature exhibit fascinating surface wettability. Biomimetics, mimicking nature for engineering solutions, provides a model for the development of functional surfaces with special wettability. Recently, bio-inspired special wetting surfaces have attracted wide scientific attention for both fundamental research and practical applications, which has become an increasingly hot research topic. This Critical Review summarizes the recent work in bio-inspired special wettability, with a focus on lotus leaf inspired self-cleaning surfaces, plants and insects inspired anisotropic superhydrophobic surfaces, mosquito eyes inspired superhydrophobic antifogging coatings, insects inspired superhydrophobic antireflection coatings, rose petals and gecko feet inspired high adhesive superhydrophobic surfaces, bio-inspired water collecting surfaces, and superlyophobic surfaces, with particular focus on the last two years. The research prospects and directions of this rapidly developing field are also briefly addressed (159 references).

Mechanically Stable Antireflection and Antifogging Coatings Fabricated by the Layer-by-Layer Deposition Process and Postcalcination

Complexes of poly(diallyldimethylammonium chloride) (PDDA) and sodium silicate (PDDA-silicate) are alternately deposited with poly(acrylic acid) (PAA) to fabricate PAA/PDDA-silicate multilayer films. The removal of the organic components in the PAA/PDDA-silicate mulilayer films through calcination produces highly porous silica coatings with excellent mechanical stability and good adhesion to substrates. Quartz substrates covered with such porous silica coatings exhibit both antireflection and antifogging properties because of the reduced refractive index and superhydrophilicity of the resultant films. A maximum transmittance of 99.86% in the visible spectral range is achieved for the calcinated PAA/PDDA-silicate films deposited on quartz substrates. The wavelengths of maximum transmittance could be well tailored by simply changing the deposition cycles of multilayer films. The usage of PDDA-silicate complexes allows for the introduction of high porosity to the resultant silica coatings, which favors the fabrication of antireflection and antifogging coatings with enhanced performance. Meanwhile, PDDA-silicate complexes enable rapid fabrication of thick porous silica coatings after calcination because of the large dimensions of the complexes in solution. The easy availability of the materials and simplicity of this method for film fabrication might make the mechanically stable multifunctional antireflection and antifogging coatings potentially useful in a variety of applications.

The Dry‐Style Antifogging Properties of Mosquito Compound Eyes and Artificial Analogues Prepared by Soft Lithography

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

Growth and alignment of polyaniline nanofibres with superhydrophobic, superhydrophilic and other properties

Polyaniline nanofibres can be prepared by a number of methods based on chemical oxidative polymerization and in situ adsorption polymerization. However, the lack of alignment in these nanostructures makes them unsuitable for many applications. Here, we report a simple approach to chemical oxidative polymerization that can control the growth and simultaneous alignment of polyaniline nanofibres grown on a range of conducting and non-conducting substrates in a wide variety of sizes. The diameters of the tips of the nanofibres can be controlled within the range 10-40 nm, and the average length can be controlled within the range 70-360 nm. Moreover, the coatings display a range of properties including superhydrophilicity and superhydrophobicity. Such nanostructured coatings may be useful for applications such as anti-fog coatings, self-cleaning surfaces, DNA manipulation, transparent electrodes for low-voltage electronics, and chemical and biological sensors.

Aspects of Energy-Saving Technology for Producing Antifogging Coatings for Light-Transmitting Materials

Aspects of Energy-Saving Technology for Producing Antifogging Coatings for Light-Transmitting Materials

Hydrophilic Layered SiO2/TiO2/WO3 Thin Film for Indoor Anti-Fogging Coatings

Hydrophilic Layered SiO2/TiO2/WO3 Thin Film for Indoor Anti-Fogging Coatings